A long felt desire in the communication, especially the multi media technology is to encounter a need for higher spectral efficiency in wireless systems.
One principal line of thought to address the OCI problem was initiated by Wyner's treatment of base station cooperation in a simple and analytically tractable model of cellular systems [11]. In this model, cells are arranged in either an infinite linear array or in some two-dimensional pattern, with interference originating only from the immediate neighboring cells (having a common edge). All the processing is performed at a single central point. Subsequent work on the information theoretic capacity of the centralized processing systems concluded that the achievable rate per user significantly exceeds that of a conventional cellular system [12,13].
Recently, decentralized detection using the belief propagation algorithm for a simple one-dimensional Wyner model was proposed in [14]. The belief propagation algorithm effectively exchanges the estimates for all signals received at each BS, by alternately exchanging likelihood values and extrinsic information. This idea was extended to 2D cellular systems in [15-17], where the limits compared to MAP decoding were studied, showing the great potential of BS cooperation with decentralized processing (at least for regular situations). Unfortunately, for a star network (commonly used today) interconnecting the BSs, this results in a huge back-haul traffic.
Another approach to convert situations where cochannel users interfere each other with comparably strong signals into an advantage for a high-frequency reuse cellular system was proposed in [18]: different BSs cooperate by sending quantized baseband signals to a single central point for joint detection and decoding. Such a distributed antenna system (DAS) not only reduces the aggregate transmitted power, but also results in much improved received SINR [19]. Using 3 appropriate receive strategies, both array and diversity gains are obtained, resulting in a substantial increase in system capacity [20, 21]. The DAS scheme, however, is less attractive for network operators due to the large amount of backhaul it requires and the cooperative scheduling necessary between the adjacent DAS units in order to avoid interference. Here, backhaul is defined as the additional communication link between different cooperating entities. Although the bandwidth of wired links used for backhaul can be very high, they are usually owned by a third party, making it attractive for the cellular system operators to reduce the backhaul in order to minimize operating costs. The influence of limited back-haul on capacity in DAS has been investigated in [22, 23].